Since CDs (Compact Discs) are easy to manufacture, are inexpensive, and are also easy to handle, they are widely used as recording media for storing various kinds of data such as digital audio data and image data, and computer programs.
In recent years, as the performance of personal computers-has improved and CD-R (CD Recordable) discs that enable additional recording and CD-RW (CD ReWritable) discs that enable data to be rewritten have appeared, the current situation is that digital data recorded on a CD can be easily copied onto such CD-R discs and CD-RW discs. Copying onto CD-R discs, etc., in this manner is generally illegal copying in which copyright is ignored. Therefore, the protection of digital data which is stored on a CD is required.
In view of the above, the present invention aims to enable an original CD to be distinguished from a copied CD, and aims to prevent a copied CD from being played back or read. In the following descriptions, it is assumed that CDs include CD-DA (CD Digital Audio) discs and CD-ROM discs.